1. Field of the Invention
The present invention relates to semiconductor light emitting technology and more particularly, to an InGaN warm white LED comprises a substrate prepared from a rare-earth garnet substrate and an activating agent prepared from cerium. Under the activation of the short-wave of InGaN, the warm white LED has the advantages of high luminous intensity, high luminous efficiency, and low temperature sensitivity.
2. Description of the Related Art
InGaN heterostructure (P-N junction) based semiconductor devices are intensively used in illumination and information technology. Various semiconductor-based multi-component, multi-color and high power luminous devices have been created and are intensively used in traffic transportation, resident houses, air ports, etc. Subject to the optical technical parameters, LED lamp surpasses conventional incandescent light sources in many fields. A booming development of LED lamp can be expected.
GaP/GaAs based LEDs are disclosed in page 480 of the book “Light Emitting Diode” (see world publication company, 1975, Russia). The book provides scientific information regarding the so-called two-element light emitting diode, i.e., heterostructure coated with phosphor to convert a primary radiation into a secondary radiation. In 1960˜70, anti-Stokes phosphor was insensitively used to convert heterostructure near-infrared radiation into visible light (red, green or blue). Further, Russian Patent N635813, filing date Dec. 9, 1977) discloses bonding possibility of InGaN-based Stockes phosphor. This phosphor has a radiation wavelength greater than the excited wavelength.
The fast development in this field should be attributed to Nichia Suji Nakamura of Nichia Chemical, Japan. In 1997, S. Nakamura issued literatures regarding InGaN heterostructures. Based on this teaching, high-performance blue, purple and ultra-purple short-wave LEDs are created.
Based on early researches, experts created white light LED on the architecture of a blue InGaN heterostructure coated with inorganic yellow phosphor. This phosphor uses the famous YAG (yttrium aluminum garnet) substrate that has the formula Y3Al5O12:Ce (see G. Blasse. Luminescence material. Amsterdam, N-Y. Pergamon 1994). This material is used as a yellow radiator in a two-element composite LED.
Conventional YAG has been intensively used. However, it still has drawbacks of (1) Insufficient quantum output ζ≦0.8; (2) When Gd+3 is introduced to substitute for a part of the yttrium in the garnet crystal lattice, the variation range of the radiation spectrum is limited; (3) Color saturation of the white radiation of the LED is insufficient, Ra≦80.
To eliminate the aforesaid drawbacks of the conventional phosphor, the inventor of the present invents a new phosphor (Taiwan Patent application no. 095149453, filed on Dec. 18, 2006). This new phosphor has N−3 and F−1 introduced therein. This patent also discloses an ideal preparation method so that the product provides high-brightness and highly saturated yellow light. When the luminous efficiency of the LED is high, the phosphor assures high luminous intensity. The prime model of this material has substantial advantages, however it still has the drawbacks of (1) Warm white light illumination cannot be reproduced, and (2) Color saturation of the overall white radiation of the LED is insufficient.